In a large saucepan, bring 2 to 3 cups of water to a simmer. Create a warm water bath by placing a heatproof glass or stainless-steel bowl over the saucepan of simmering water. Add the chocolate chips and heavy cream to the bowl. Mix well with a spatula to combine as the chocolate melts.
Remove the bowl from the heat and transfer the chocolate mixture to a parchment paper– lined loaf pan or shallow bowl and cool completely to room temperature. Place in to the fridge for 90 minutes to solidify.
Using a small melon baller, scoop out the truffle mixture and mold into 1-inch balls. If you don’t have a melon baller, use your hands.
Fill a small bowl with the crushed pistachios, roll the truffles in the pistachios, pressing the nuts gently into the surface. Using a fine-mesh strainer or sifter, dust the truffles with the matcha powder.